1. Field of the Invention
The invention relates to a method for the determination of the saturation of the blood of a living organism with oxygen, in which radiation in a first and in a second wavelength range, in which the absorption coefficients of oxyhaemoglobin (HBO.sub.2), on the one hand, and reduced haemoglobin (Hb), on the other hand, show different ratios, is simultaneously beamed into living tissue, and the mixed residual radiation emanating from the irradiated tissue is received and measured in two different wavelength measuring ranges by two optoelectronic receiver elements, and, on the basis of these measurements, the intensities of the residual light in the two wavelength ranges are determined.
2. Description of the Related Art
Methods of this kind are known. Determination of the oxygen saturation by known methods is, for example, described in detail in the chapter "NON-INVASIVE SPECTROPHOTOMETRIC ESTIMATION OF ARTERIAL OXYGEN SATURATION" of the book "Non-Invasive Measurements" by I. Yoshiya and Y. Shimada, published by Academic Press Inc. in 1983.
To determine the oxygen saturation, precise values for the residual radiation of two different wavelengths are, however, required. If radiation of two different wavelength ranges is beamed simultaneously into the tissue, the two components get mixed. Consequently, when the residual radiation is then received in the optoelectronic receiver elements, one wavelength range has to be filtered out in each optoelectronic receiver element. However, as mentioned above, the two wavelength ranges for the determination of the oxygen saturation cannot be selected arbitrarily. It is, therefore, not possible to assume that wavelength ranges will be selected for which suitable filters are available at reasonable cost. The conditions involved are particularly difficult to meet if for physical reasons the optoelectronic elements and filters have to be as small as possible as is the case, for example, for measurements at an earlobe, a finger or a toe.
It is also known that the radiation of the two wavelength ranges employed can be separated by pulsed alternate beaming of the radiation of the two wavelength ranges so at any instant in time radiation of one wavelength range only will be beamed through the tissue. Difficulties in circuit technology do, however, result in this case since the pulse frequency of the blood also has to be taken into account and to some extent the results have to be stored.